3 Pumpkin - Notes on handling the Perl Patch Pumpkin And Porting Perl
7 There is no simple synopsis, yet.
11 This document attempts to begin to describe some of the considerations
12 involved in patching, porting, and maintaining perl.
14 This document is still under construction, and still subject to
15 significant changes. Still, I hope parts of it will be useful,
16 so I'm releasing it even though it's not done.
18 For the most part, it's a collection of anecdotal information that
19 already assumes some familiarity with the Perl sources. I really need
20 an introductory section that describes the organization of the sources
21 and all the various auxiliary files that are part of the distribution.
23 =head1 Where Do I Get Perl Sources and Related Material?
25 The Comprehensive Perl Archive Network (or CPAN) is the place to go.
26 There are many mirrors, but the easiest thing to use is probably
27 http://www.cpan.org/README.html , which automatically points you to a
28 mirror site "close" to you.
30 =head2 Perl5-porters mailing list
32 The mailing list perl5-porters@perl.org
33 is the main group working with the development of perl. If you're
34 interested in all the latest developments, you should definitely
35 subscribe. The list is high volume, but generally has a
36 fairly low noise level.
38 Subscribe by sending the message (in the body of your letter)
40 subscribe perl5-porters
42 to perl5-porters-request@perl.org .
44 Archives of the list are held at:
46 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
48 =head1 How are Perl Releases Numbered?
50 Beginning with v5.6.0, even versions will stand for maintenance releases
51 and odd versions for development releases, i.e., v5.6.x for maintenance
52 releases, and v5.7.x for development releases. Before v5.6.0, subversions
53 _01 through _49 were reserved for bug-fix maintenance releases, and
54 subversions _50 through _99 for unstable development versions.
56 For example, in v5.6.1, the revision number is 5, the version is 6,
57 and 1 is the subversion.
59 For compatibility with the older numbering scheme the composite floating
60 point version number continues to be available as the magic variable $],
61 and amounts to C<$revision + $version/1000 + $subversion/100000>. This
62 can still be used in comparisons.
64 print "You've got an old perl\n" if $] < 5.005_03;
66 In addition, the version is also available as a string in $^V.
68 print "You've got a new perl\n" if $^V and $^V ge v5.6.0;
70 You can also require particular version (or later) with:
74 or using the new syntax available only from v5.6 onward:
78 At some point in the future, we may need to decide what to call the
79 next big revision. In the .package file used by metaconfig to
80 generate Configure, there are two variables that might be relevant:
81 $baserev=5 and $package=perl5.
83 Perl releases produced by the members of perl5-porters are usually
84 available on CPAN in the F<src/5.0/maint> and F<src/5.0/devel>
87 =head2 Maintenance and Development Subversions
89 The first rule of maintenance work is "First, do no harm."
91 Trial releases of bug-fix maintenance releases are announced on
92 perl5-porters. Trial releases use the new subversion number (to avoid
93 testers installing it over the previous release) and include a 'local
94 patch' entry in patchlevel.h. The distribution file contains the
95 string C<MAINT_TRIAL> to make clear that the file is not meant for
98 In general, the names of official distribution files for the public
99 always match the regular expression:
101 ^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
103 C<$1> in the pattern is always an even number for maintenance
104 versions, and odd for developer releases.
106 In the past it has been observed that pumpkings tend to invent new
107 naming conventions on the fly. If you are a pumpking, before you
108 invent a new name for any of the three types of perl distributions,
109 please inform the guys from the CPAN who are doing indexing and
110 provide the trees of symlinks and the like. They will have to know
111 I<in advance> what you decide.
113 =head2 Why is it called the patch pumpkin?
115 Chip Salzenberg gets credit for that, with a nod to his cow orker,
116 David Croy. We had passed around various names (baton, token, hot
117 potato) but none caught on. Then, Chip asked:
121 Who has the patch pumpkin?
123 To explain: David Croy once told me once that at a previous job,
124 there was one tape drive and multiple systems that used it for backups.
125 But instead of some high-tech exclusion software, they used a low-tech
126 method to prevent multiple simultaneous backups: a stuffed pumpkin.
127 No one was allowed to make backups unless they had the "backup pumpkin".
133 =head1 Philosophical Issues in Patching and Porting Perl
135 There are no absolute rules, but there are some general guidelines I
136 have tried to follow as I apply patches to the perl sources.
137 (This section is still under construction.)
139 =head2 Solve problems as generally as possible
141 Never implement a specific restricted solution to a problem when you
142 can solve the same problem in a more general, flexible way.
144 For example, for dynamic loading to work on some SVR4 systems, we had
145 to build a shared libperl.so library. In order to build "FAT" binaries
146 on NeXT 4.0 systems, we had to build a special libperl library. Rather
147 than continuing to build a contorted nest of special cases, I
148 generalized the process of building libperl so that NeXT and SVR4 users
149 could still get their work done, but others could build a shared
150 libperl if they wanted to as well.
152 Contain your changes carefully. Assume nothing about other operating
153 systems, not even closely related ones. Your changes must not affect
156 Spy shamelessly on how similar patching or porting issues have been
159 If feasible, try to keep filenames 8.3-compliant to humor those poor
160 souls that get joy from running Perl under such dire limitations.
161 There's a script, check83.pl, for keeping your nose 8.3-clean.
162 In a similar vein, do not create files or directories which differ only
163 in case (upper versus lower).
165 =head2 Seek consensus on major changes
167 If you are making big changes, don't do it in secret. Discuss the
168 ideas in advance on perl5-porters.
170 =head2 Keep the documentation up-to-date
172 If your changes may affect how users use perl, then check to be sure
173 that the documentation is in sync with your changes. Be sure to
174 check all the files F<pod/*.pod> and also the F<INSTALL> document.
176 Consider writing the appropriate documentation first and then
177 implementing your change to correspond to the documentation.
179 =head2 Avoid machine-specific #ifdef's
181 To the extent reasonable, try to avoid machine-specific #ifdef's in
182 the sources. Instead, use feature-specific #ifdef's. The reason is
183 that the machine-specific #ifdef's may not be valid across major
184 releases of the operating system. Further, the feature-specific tests
185 may help out folks on another platform who have the same problem.
187 =head2 Machine-specific files
193 If you have many machine-specific #defines or #includes, consider
194 creating an "osish.h" (os2ish.h, vmsish.h, and so on) and including
195 that in perl.h. If you have several machine-specific files (function
196 emulations, function stubs, build utility wrappers) you may create a
197 separate subdirectory (djgpp, win32) and put the files in there.
198 Remember to update C<MANIFEST> when you add files.
200 If your system supports dynamic loading but none of the existing
201 methods at F<ext/DynaLoader/dl_*.xs> work for you, you must write
202 a new one. Study the existing ones to see what kind of interface
207 There are two kinds of hints: hints for building Perl and hints for
208 extensions. The former live in the C<hints> subdirectory, the latter
209 in C<ext/*/hints> subdirectories.
211 The top level hints are Bourne-shell scripts that set, modify and
212 unset appropriate Configure variables, based on the Configure command
213 line options and possibly existing config.sh and Policy.sh files from
214 previous Configure runs.
216 The extension hints are written in Perl (by the time they are used
217 miniperl has been built) and control the building of their respective
218 extensions. They can be used to for example manipulate compilation
221 =item build and installation Makefiles, scripts, and so forth
223 Sometimes you will also need to tweak the Perl build and installation
224 procedure itself, like for example F<Makefile.SH> and F<installperl>.
225 Tread very carefully, even more than usual. Contain your changes
230 Many of the tests in C<t> subdirectory assume machine-specific things
231 like existence of certain functions, something about filesystem
232 semantics, certain external utilities and their error messages. Use
233 the C<$^O> and the C<Config> module (which contains the results of the
234 Configure run, in effect the C<config.sh> converted to Perl) to either
235 skip (preferably not) or customize (preferable) the tests for your
240 Certain standard modules may need updating if your operating system
241 sports for example a native filesystem naming. You may want to update
242 some or all of the modules File::Basename, File::Spec, File::Path, and
243 File::Copy to become aware of your native filesystem syntax and
246 Remember to have a $VERSION in the modules. You can use the
247 Porting/checkVERSION.pl script for checking this.
251 If your operating system comes from outside UNIX you almost certainly
252 will have differences in the available operating system functionality
253 (missing system calls, different semantics, whatever). Please
254 document these at F<pod/perlport.pod>. If your operating system is
255 the first B<not> to have a system call also update the list of
256 "portability-bewares" at the beginning of F<pod/perlfunc.pod>.
258 A file called F<README.youros> at the top level that explains things
259 like how to install perl at this platform, where to get any possibly
260 required additional software, and for example what test suite errors
261 to expect, is nice too. Such files are in the process of being written
262 in pod format and will eventually be renamed F<INSTALL.youros>.
264 You may also want to write a separate F<.pod> file for your operating
265 system to tell about existing mailing lists, os-specific modules,
266 documentation, whatever. Please name these along the lines of
267 F<perl>I<youros>.pod. [unfinished: where to put this file (the pod/
268 subdirectory, of course: but more importantly, which/what index files
273 =head2 Allow for lots of testing
275 We should never release a main version without testing it as a
278 =head2 Test popular applications and modules.
280 We should never release a main version without testing whether or not
281 it breaks various popular modules and applications. A partial list of
282 such things would include majordomo, metaconfig, apache, Tk, CGI,
283 libnet, and libwww, to name just a few. Of course it's quite possible
284 that some of those things will be just plain broken and need to be fixed,
285 but, in general, we ought to try to avoid breaking widely-installed
288 =head2 Automated generation of derivative files
290 The F<embed.h>, F<keywords.h>, F<opcode.h>, and F<perltoc.pod> files
291 are all automatically generated by perl scripts. In general, don't
292 patch these directly; patch the data files instead.
294 F<Configure> and F<config_h.SH> are also automatically generated by
295 B<metaconfig>. In general, you should patch the metaconfig units
296 instead of patching these files directly. However, very minor changes
297 to F<Configure> may be made in between major sync-ups with the
298 metaconfig units, which tends to be complicated operations. But be
299 careful, this can quickly spiral out of control. Running metaconfig
302 Also F<Makefile> is automatically produced from F<Makefile.SH>.
303 In general, look out for all F<*.SH> files.
305 Finally, the sample files in the F<Porting/> subdirectory are
306 generated automatically by the script F<U/mksample> included
307 with the metaconfig units. See L<"run metaconfig"> below for
308 information on obtaining the metaconfig units.
310 =head1 How to Make a Distribution
312 This section has now been expanded and moved into its own file,
313 F<Porting/release_managers_guide.pod>.
315 I've kept some of the subsections here for now, as they don't direclty
316 eleate to building a release any more, but still contain what might be
317 useful information - DAPM 7/2009.
319 =head2 run metaconfig
321 If you need to make changes to Configure or config_h.SH, it may be best to
322 change the appropriate metaconfig units instead, and regenerate Configure.
326 will regenerate Configure and config_h.SH. Much more information
327 on obtaining and running metaconfig is in the F<U/README> file
328 that comes with Perl's metaconfig units.
330 Since metaconfig is hard to change, running correction scripts after
331 this generation is sometimes needed. Configure gained complexity over
332 time, and the order in which config_h.SH is generated can cause havoc
333 when compiling perl. Therefor, you need to run Porting/config_h.pl
334 after that generation. All that and more is described in the README
335 files that come with the metaunits.
337 Perl's metaconfig units should be available on CPAN. A set of units
338 that will work with perl5.9.x is in a file with a name similar to
339 F<mc_units-20070423.tgz> under http://www.cpan.org/authors/id/H/HM/HMBRAND/ .
340 The mc_units tar file should be unpacked in your main perl source directory.
341 Note: those units were for use with 5.9.x. There may have been changes since
342 then. Check for later versions or contact perl5-porters@perl.org to obtain a
343 pointer to the current version.
345 Alternatively, do consider if the F<*ish.h> files or the hint files might be
346 a better place for your changes.
350 If you are using metaconfig to regenerate Configure, then you should note
351 that metaconfig actually uses MANIFEST.new, so you want to be sure
352 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
353 distinction particularly useful, but that's probably because I still haven't
354 learned how to use the full suite of tools in the dist distribution.
359 This will build a config.sh and config.h. You can skip this if you haven't
360 changed Configure or config_h.SH at all. I use the following command
362 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
364 -Dcf_email='yourname@yourhost.yourplace.com' \
365 -Dperladmin='yourname@yourhost.yourplace.com' \
366 -Dmydomain='.yourplace.com' \
367 -Dmyhostname='yourhost' \
370 =head2 Update Porting/config.sh and Porting/config_H
373 This section needs revision. We're currently working on easing
374 the task of keeping the vms, win32, and plan9 config.sh info
375 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
376 files in the appropriate subdirectories and then generate 'canned'
377 config.h files for vms, win32, etc. from the generic config.sh file.
378 This is to ease maintenance. When Configure gets updated, the parts
379 sometimes get scrambled around, and the changes in config_H can
380 sometimes be very hard to follow. config.sh, on the other hand, can
381 safely be sorted, so it's easy to track (typically very small) changes
382 to config.sh and then propagate them to a canned 'config.h' by any
383 number of means, including a perl script in win32/ or carrying
384 config.sh and config_h.SH to a Unix system and running sh
385 config_h.SH.) Vms uses configure.com to generate its own config.sh
386 and config.h. If you want to add a new variable to config.sh check
387 with vms folk how to add it to configure.com too.
390 The Porting/config.sh and Porting/config_H files are provided to
391 help those folks who can't run Configure. It is important to keep
392 them up-to-date. If you have changed config_h.SH, those changes must
393 be reflected in config_H as well. (The name config_H was chosen to
394 distinguish the file from config.h even on case-insensitive file systems.)
395 Simply edit the existing config_H file; keep the first few explanatory
396 lines and then copy your new config.h below.
398 It may also be necessary to update win32/config.?c, and
399 plan9/config.plan9, though you should be quite careful in doing so if
400 you are not familiar with those systems. You might want to issue your
401 patch with a promise to quickly issue a follow-up that handles those
404 =head2 make regen_perly
406 If perly.y has been edited, it is necessary to run this target to rebuild
407 perly.h, perly.act and perly.tab. In fact this target just runs the Perl
408 script regen_perly.pl. Note that perly.c is I<not> rebuilt; this is just a
409 plain static file now.
411 This target relies on you having Bison installed on your system. Running
412 the target will tell you if you haven't got the right version, and if so,
413 where to get the right one. Or if you prefer, you could hack
414 regen_perly.pl to work with your version of Bison. The important things
415 are that the regexes can still extract out the right chunks of the Bison
416 output into perly.act and perly.tab, and that the contents of those two
417 files, plus perly.h, are functionally equivalent to those produced by the
418 supported version of Bison.
420 Note that in the old days, you had to do C<make run_byacc> instead.
422 =head2 make regen_all
424 This target takes care of the regen_headers target.
425 (It used to also call the regen_pods target, but that has been eliminated.)
427 =head2 make regen_headers
429 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
430 generated by perl scripts. Since the user isn't guaranteed to have a
431 working perl, we can't require the user to generate them. Hence you have
432 to, if you're making a distribution.
434 I used to include rules like the following in the makefile:
436 # The following three header files are generated automatically
437 # The correct versions should be already supplied with the perl kit,
438 # in case you don't have perl or 'sh' available.
439 # The - is to ignore error return codes in case you have the source
440 # installed read-only or you don't have perl yet.
441 keywords.h: keywords.pl
442 @echo "Don't worry if this fails."
446 However, I got B<lots> of mail consisting of people worrying because the
447 command failed. I eventually decided that I would save myself time
448 and effort by manually running C<make regen_headers> myself rather
449 than answering all the questions and complaints about the failing
452 =head2 global.sym, interp.sym and perlio.sym
454 Make sure these files are up-to-date. Read the comments in these
455 files and in perl_exp.SH to see what to do.
457 =head2 Binary compatibility
459 If you do change F<global.sym> or F<interp.sym>, think carefully about
460 what you are doing. To the extent reasonable, we'd like to maintain
461 source and binary compatibility with older releases of perl. That way,
462 extensions built under one version of perl will continue to work with
463 new versions of perl.
465 Of course, some incompatible changes may well be necessary. I'm just
466 suggesting that we not make any such changes without thinking carefully
467 about them first. If possible, we should provide
468 backwards-compatibility stubs. There's a lot of XS code out there.
469 Let's not force people to keep changing it.
473 F<ext/Devel-PPPort/PPPort.pm> needs to be synchronized to include all
474 new macros added to .h files (normally perl.h and XSUB.h, but others
475 as well). Since chances are that when a new macro is added the
476 committer will forget to update F<PPPort.pm>, it's the best to diff for
477 changes in .h files when making a new release and making sure that
478 F<PPPort.pm> contains them all.
480 The pumpking can delegate the synchronization responsibility to anybody
481 else, but the release process is the only place where we can make sure
482 that no new macros fell through the cracks.
487 The F<pod/perltodo.pod> file contains a roughly-categorized unordered
488 list of aspects of Perl that could use enhancement, features that could
489 be added, areas that could be cleaned up, and so on. During your term
490 as pumpkin-holder, you will probably address some of these issues, and
491 perhaps identify others which, while you decide not to address them this
492 time around, may be tackled in the future. Update the file to reflect
493 the situation as it stands when you hand over the pumpkin.
495 You might like, early in your pumpkin-holding career, to see if you
496 can find champions for particular issues on the to-do list: an issue
497 owned is an issue more likely to be resolved.
499 There are also some more porting-specific L</Todo> items later in this
502 =head2 OS/2-specific updates
504 In the os2 directory is F<diff.configure>, a set of OS/2-specific
505 diffs against B<Configure>. If you make changes to Configure, you may
506 want to consider regenerating this diff file to save trouble for the
509 You can also consider the OS/2 diffs as reminders of portability
510 things that need to be fixed in Configure.
512 =head2 VMS-specific updates
514 The Perl revision number appears as "perl5" in configure.com.
515 It is courteous to update that if necessary.
518 =head2 Making a new patch
520 I find the F<makepatch> utility quite handy for making patches.
521 You can obtain it from any CPAN archive under
522 http://www.cpan.org/authors/Johan_Vromans/ . There are a couple
523 of differences between my version and the standard one. I have mine do
526 # Print a reassuring "End of Patch" note so people won't
527 # wonder if their mailer truncated patches.
528 print "\n\nEnd of Patch.\n";
530 at the end. That's because I used to get questions from people asking
531 if their mail was truncated.
533 It also writes Index: lines which include the new directory prefix
534 (change Index: print, approx line 294 or 310 depending on the version,
535 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
536 work with more POSIX conformant patch programs.
538 Here's how I generate a new patch. I'll use the hypothetical
539 5.004_07 to 5.004_08 patch as an example.
541 # unpack perl5.004_07/
542 gzip -d -c perl5.004_07.tar.gz | tar -xof -
543 # unpack perl5.004_08/
544 gzip -d -c perl5.004_08.tar.gz | tar -xof -
545 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
547 Makepatch will automatically generate appropriate B<rm> commands to remove
548 deleted files. Unfortunately, it will not correctly set permissions
549 for newly created files, so you may have to do so manually. For example,
550 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
551 so at the top of the patch, I inserted the following lines:
557 Now, of course, my patch is now wrong because makepatch didn't know I
558 was going to do that command, and it patched against /dev/null.
560 So, what I do is sort out all such shell commands that need to be in the
561 patch (including possible mv-ing of files, if needed) and put that in the
562 shell commands at the top of the patch. Next, I delete all the patch parts
563 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
567 sh ../perl5.004_08.pat
569 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
571 (Note the append to preserve my shell commands.)
572 Now, my patch will line up with what the end users are going to do.
574 =head2 Testing your patch
576 It seems obvious, but be sure to test your patch. That is, verify that
577 it produces exactly the same thing as your full distribution.
580 gzip -d -c perl5.004_07.tar.gz | tar -xf -
582 sh ../perl5.004_08.pat
583 patch -p1 -N < ../perl5.004_08.pat
585 gdiff -r perl5.004_07 perl5.004_08
587 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
591 Again, it's obvious, but you should test your new version as widely as you
592 can. You can be sure you'll hear about it quickly if your version doesn't
593 work on both ANSI and pre-ANSI compilers, and on common systems such as
594 SunOS 4.1.[34], Solaris, and Linux.
596 If your changes include conditional code, try to test the different
597 branches as thoroughly as you can. For example, if your system
598 supports dynamic loading, you can also test static loading with
602 You can also hand-tweak your config.h to try out different #ifdef
609 =item gcc -ansi -pedantic
611 Configure -Dgccansipedantic [ -Dcc=gcc ] will enable (via the cflags script,
612 not $Config{ccflags}) the gcc strict ANSI C flags -ansi and -pedantic for
613 the compilation of the core files on platforms where it knows it can
614 do so (like Linux, see cflags.SH for the full list), and on some
615 platforms only one (Solaris can do only -pedantic, not -ansi).
616 The flag -DPERL_GCC_PEDANTIC also gets added, since gcc does not add
617 any internal cpp flag to signify that -pedantic is being used, as it
618 does for -ansi (__STRICT_ANSI__).
620 Note that the -ansi and -pedantic are enabled only for version 3 (and
621 later) of gcc, since even gcc version 2.95.4 finds lots of seemingly
622 false "value computed not used" errors from Perl.
624 The -ansi and -pedantic are useful in catching at least the following
625 nonportable practices:
631 gcc-specific extensions
647 The -Dgccansipedantic should be used only when cleaning up the code,
648 not for production builds, since otherwise gcc cannot inline certain
653 =head1 Running Purify
655 Purify is a commercial tool that is helpful in identifying memory
656 overruns, wild pointers, memory leaks and other such badness. Perl
657 must be compiled in a specific way for optimal testing with Purify.
659 Use the following commands to test perl with Purify:
661 sh Configure -des -Doptimize=-g -Uusemymalloc -Dusemultiplicity \
663 setenv PURIFYOPTIONS "-chain-length=25"
666 ln -s ../pureperl perl
667 setenv PERL_DESTRUCT_LEVEL 2
670 Disabling Perl's malloc allows Purify to monitor allocations and leaks
671 more closely; using Perl's malloc will make Purify report most leaks
672 in the "potential" leaks category. Enabling the multiplicity option
673 allows perl to clean up thoroughly when the interpreter shuts down, which
674 reduces the number of bogus leak reports from Purify. The -DPURIFY
675 enables any Purify-specific debugging code in the sources.
677 Purify outputs messages in "Viewer" windows by default. If you don't have
678 a windowing environment or if you simply want the Purify output to
679 unobtrusively go to a log file instead of to the interactive window,
680 use the following options instead:
682 setenv PURIFYOPTIONS "-chain-length=25 -windows=no -log-file=perl.log \
685 The only currently known leaks happen when there are compile-time errors
686 within eval or require. (Fixing these is non-trivial, unfortunately, but
687 they must be fixed eventually.)
689 =head1 Common Gotchas
693 =item Probably Prefer POSIX
695 It's often the case that you'll need to choose whether to do
696 something the BSD-ish way or the POSIX-ish way. It's usually not
697 a big problem when the two systems use different names for similar
698 functions, such as memcmp() and bcmp(). The perl.h header file
699 handles these by appropriate #defines, selecting the POSIX mem*()
700 functions if available, but falling back on the b*() functions, if
703 More serious is the case where some brilliant person decided to
704 use the same function name but give it a different meaning or
705 calling sequence :-). getpgrp() and setpgrp() come to mind.
706 These are a real problem on systems that aim for conformance to
707 one standard (e.g. POSIX), but still try to support the other way
708 of doing things (e.g. BSD). My general advice (still not really
709 implemented in the source) is to do something like the following.
710 Suppose there are two alternative versions, fooPOSIX() and
714 /* use fooPOSIX(); */
717 /* try to emulate fooPOSIX() with fooBSD();
718 perhaps with the following: */
719 # define fooPOSIX fooBSD
721 # /* Uh, oh. We have to supply our own. */
722 # define fooPOSIX Perl_fooPOSIX
726 =item Think positively
728 If you need to add an #ifdef test, it is usually easier to follow if you
729 think positively, e.g.
731 #ifdef HAS_NEATO_FEATURE
732 /* use neato feature */
734 /* use some fallback mechanism */
737 rather than the more impenetrable
739 #ifndef MISSING_NEATO_FEATURE
740 /* Not missing it, so we must have it, so use it */
742 /* Are missing it, so fall back on something else. */
745 Of course for this toy example, there's not much difference. But when
746 the #ifdef's start spanning a couple of screen fulls, and the #else's
747 are marked something like
749 #else /* !MISSING_NEATO_FEATURE */
751 I find it easy to get lost.
753 =item Providing Missing Functions -- Problem
755 Not all systems have all the neat functions you might want or need, so
756 you might decide to be helpful and provide an emulation. This is
757 sound in theory and very kind of you, but please be careful about what
758 you name the function. Let me use the C<pause()> function as an
761 Perl5.003 has the following in F<perl.h>
764 #define pause() sleep((32767<<16)+32767)
767 Configure sets HAS_PAUSE if the system has the pause() function, so
768 this #define only kicks in if the pause() function is missing.
771 Unfortunately, some systems apparently have a prototype for pause()
772 in F<unistd.h>, but don't actually have the function in the library.
773 (Or maybe they do have it in a library we're not using.)
775 Thus, the compiler sees something like
777 extern int pause(void);
779 #define pause() sleep((32767<<16)+32767)
781 and dies with an error message. (Some compilers don't mind this;
782 others apparently do.)
784 To work around this, 5.003_03 and later have the following in perl.h:
786 /* Some unistd.h's give a prototype for pause() even though
787 HAS_PAUSE ends up undefined. This causes the #define
788 below to be rejected by the compiler. Sigh.
793 # define Pause() sleep((32767<<16)+32767)
798 The curious reader may wonder why I didn't do the following in
804 sleep((32767<<16)+32767);
808 That is, since the function is missing, just provide it.
809 Then things would probably be been alright, it would seem.
811 Well, almost. It could be made to work. The problem arises from the
812 conflicting needs of dynamic loading and namespace protection.
814 For dynamic loading to work on AIX (and VMS) we need to provide a list
815 of symbols to be exported. This is done by the script F<perl_exp.SH>,
816 which reads F<global.sym> and F<interp.sym>. Thus, the C<pause>
817 symbol would have to be added to F<global.sym> So far, so good.
819 On the other hand, one of the goals of Perl5 is to make it easy to
820 either extend or embed perl and link it with other libraries. This
821 means we have to be careful to keep the visible namespace "clean".
822 That is, we don't want perl's global variables to conflict with
823 those in the other application library. Although this work is still
824 in progress, the way it is currently done is via the F<embed.h> file.
825 This file is built from the F<global.sym> and F<interp.sym> files,
826 since those files already list the globally visible symbols. If we
827 had added C<pause> to global.sym, then F<embed.h> would contain the
830 #define pause Perl_pause
832 and calls to C<pause> in the perl sources would now point to
833 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
834 it will go looking for C<perl_pause>, which probably won't exist in any
835 of the standard libraries. Thus the build of perl will fail.
837 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
838 since they would get a C<Perl_pause> function in util.c. The rest of
839 the world would be in trouble.
841 And yes, this scenario has happened. On SCO, the function C<chsize>
842 is available. (I think it's in F<-lx>, the Xenix compatibility
843 library.) Since the perl4 days (and possibly before), Perl has
844 included a C<chsize> function that gets called something akin to
847 I32 chsize(fd, length)
853 #define chsize Perl_chsize
855 to F<embed.h>, the compile started failing on SCO systems.
857 The "fix" is to give the function a different name. The one
858 implemented in 5.003_05 isn't optimal, but here's what was done:
861 # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */
864 # define my_chsize chsize
867 My explanatory comment in patch 5.003_05 said:
869 Undef and then re-define my_chsize from Perl_my_chsize to
870 just plain chsize if this system HAS_CHSIZE. This probably only
871 applies to SCO. This shows the perils of having internal
872 functions with the same name as external library functions :-).
874 Now, we can safely put C<my_chsize> in F<global.sym>, export it, and
875 hide it with F<embed.h>.
877 To be consistent with what I did for C<pause>, I probably should have
878 called the new function C<Chsize>, rather than C<my_chsize>.
879 However, the perl sources are quite inconsistent on this (Consider
880 New, Mymalloc, and Myremalloc, to name just a few.)
882 There is a problem with this fix, however, in that C<Perl_chsize>
883 was available as a F<libperl.a> library function in 5.003, but it
884 isn't available any more (as of 5.003_07). This means that we've
885 broken binary compatibility. This is not good.
887 =item Providing missing functions -- some ideas
889 We currently don't have a standard way of handling such missing
890 function names. Right now, I'm effectively thinking aloud about a
891 solution. Some day, I'll try to formally propose a solution.
893 Part of the problem is that we want to have some functions listed as
894 exported but not have their names mangled by embed.h or possibly
895 conflict with names in standard system headers. We actually already
896 have such a list at the end of F<perl_exp.SH> (though that list is
899 # extra globals not included above.
900 cat <<END >> perl.exp
924 This still needs much thought, but I'm inclined to think that one
925 possible solution is to prefix all such functions with C<perl_> in the
926 source and list them along with the other C<perl_*> functions in
929 Thus, for C<chsize>, we'd do something like the following:
933 # define perl_chsize chsize
936 then in some file (e.g. F<util.c> or F<doio.c>) do
939 I32 perl_chsize(fd, length)
940 /* implement the function here . . . */
943 Alternatively, we could just always use C<chsize> everywhere and move
944 C<chsize> from F<global.sym> to the end of F<perl_exp.SH>. That would
945 probably be fine as long as our C<chsize> function agreed with all the
946 C<chsize> function prototypes in the various systems we'll be using.
947 As long as the prototypes in actual use don't vary that much, this is
948 probably a good alternative. (As a counter-example, note how Configure
949 and perl have to go through hoops to find and use get Malloc_t and
950 Free_t for C<malloc> and C<free>.)
952 At the moment, this latter option is what I tend to prefer.
954 =item All the world's a VAX
956 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
957 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
958 common (do you have any idea how many systems run SCO?) If you don't
959 have a bunch of v7 manuals handy, the metaconfig units (by default
960 installed in F</usr/local/lib/dist/U>) are a good resource to look at
965 =head1 Miscellaneous Topics
969 Why does perl use a metaconfig-generated Configure script instead of an
970 autoconf-generated configure script?
972 Metaconfig and autoconf are two tools with very similar purposes.
973 Metaconfig is actually the older of the two, and was originally written
974 by Larry Wall, while autoconf is probably now used in a wider variety of
975 packages. The autoconf info file discusses the history of autoconf and
976 how it came to be. The curious reader is referred there for further
979 Overall, both tools are quite good, I think, and the choice of which one
980 to use could be argued either way. In March, 1994, when I was just
981 starting to work on Configure support for Perl5, I considered both
982 autoconf and metaconfig, and eventually decided to use metaconfig for the
987 =item Compatibility with Perl4
989 Perl4 used metaconfig, so many of the #ifdef's were already set up for
990 metaconfig. Of course metaconfig had evolved some since Perl4's days,
991 but not so much that it posed any serious problems.
993 =item Metaconfig worked for me
995 My system at the time was Interactive 2.2, an SVR3.2/386 derivative that
996 also had some POSIX support. Metaconfig-generated Configure scripts
997 worked fine for me on that system. On the other hand, autoconf-generated
998 scripts usually didn't. (They did come quite close, though, in some
999 cases.) At the time, I actually fetched a large number of GNU packages
1000 and checked. Not a single one configured and compiled correctly
1001 out-of-the-box with the system's cc compiler.
1003 =item Configure can be interactive
1005 With both autoconf and metaconfig, if the script works, everything is
1006 fine. However, one of my main problems with autoconf-generated scripts
1007 was that if it guessed wrong about something, it could be B<very> hard to
1008 go back and fix it. For example, autoconf always insisted on passing the
1009 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
1010 wanted or needed for that package. There was no way short of editing the
1011 configure script to turn this off. You couldn't just edit the resulting
1012 Makefile at the end because the -Xp flag influenced a number of other
1015 Metaconfig's Configure scripts, on the other hand, can be interactive.
1016 Thus if Configure is guessing things incorrectly, you can go back and fix
1017 them. This isn't as important now as it was when we were actively
1018 developing Configure support for new features such as dynamic loading,
1019 but it's still useful occasionally.
1023 At the time, autoconf-generated scripts were covered under the GNU Public
1024 License, and hence weren't suitable for inclusion with Perl, which has a
1025 different licensing policy. (Autoconf's licensing has since changed.)
1029 Metaconfig builds up Configure from a collection of discrete pieces
1030 called "units". You can override the standard behavior by supplying your
1031 own unit. With autoconf, you have to patch the standard files instead.
1032 I find the metaconfig "unit" method easier to work with. Others
1033 may find metaconfig's units clumsy to work with.
1037 =head2 Why isn't there a directory to override Perl's library?
1039 Mainly because no one's gotten around to making one. Note that
1040 "making one" involves changing perl.c, Configure, config_h.SH (and
1041 associated files, see above), and I<documenting> it all in the
1044 Apparently, most folks who want to override one of the standard library
1045 files simply do it by overwriting the standard library files.
1049 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1050 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1051 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1052 a mail message from Larry:
1054 The main intent of APPLLIB_EXP is for folks who want to send out a
1055 version of Perl embedded in their product. They would set the symbol
1056 to be the name of the library containing the files needed to run or to
1057 support their particular application. This works at the "override"
1058 level to make sure they get their own versions of any library code that
1059 they absolutely must have configuration control over.
1061 As such, I don't see any conflict with a sysadmin using it for a
1062 override-ish sort of thing, when installing a generic Perl. It should
1063 probably have been named something to do with overriding though. Since
1064 it's undocumented we could still change it... :-)
1066 Given that it's already there, you can use it to override distribution modules.
1067 One way to do that is to add
1069 ccflags="$ccflags -DAPPLLIB_EXP=\"/my/override\""
1071 to your config.over file. (You have to be particularly careful to get the
1072 double quotes in. APPLLIB_EXP must be a valid C string. It might
1073 actually be easier to just #define it yourself in perl.c.)
1075 Then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB. Perl will
1076 also search architecture-specific and version-specific subdirectories of
1079 =head2 Shared libperl.so location
1081 Why isn't the shared libperl.so installed in /usr/lib/ along
1082 with "all the other" shared libraries? Instead, it is installed
1083 in $archlib, which is typically something like
1085 /usr/local/lib/perl5/archname/5.00404
1087 and is architecture- and version-specific.
1089 The basic reason why a shared libperl.so gets put in $archlib is so that
1090 you can have more than one version of perl on the system at the same time,
1091 and have each refer to its own libperl.so.
1093 Three examples might help. All of these work now; none would work if you
1094 put libperl.so in /usr/lib.
1100 Suppose you want to have both threaded and non-threaded perl versions
1101 around. Configure will name both perl libraries "libperl.so" (so that
1102 you can link to them with -lperl). The perl binaries tell them apart
1103 by having looking in the appropriate $archlib directories.
1107 Suppose you have perl5.004_04 installed and you want to try to compile
1108 it again, perhaps with different options or after applying a patch.
1109 If you already have libperl.so installed in /usr/lib/, then it may be
1110 either difficult or impossible to get ld.so to find the new libperl.so
1111 that you're trying to build. If, instead, libperl.so is tucked away in
1112 $archlib, then you can always just change $archlib in the current perl
1113 you're trying to build so that ld.so won't find your old libperl.so.
1114 (The INSTALL file suggests you do this when building a debugging perl.)
1118 The shared perl library is not a "well-behaved" shared library with
1119 proper major and minor version numbers, so you can't necessarily
1120 have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
1121 perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
1122 were to install /usr/lib/libperl.so.4.5. Now, when you try to run
1123 perl5.004_04, ld.so might try to load libperl.so.4.5, since it has
1124 the right "major version" number. If this works at all, it almost
1125 certainly defeats the reason for keeping perl5.004_04 around. Worse,
1126 with development subversions, you certaily can't guarantee that
1127 libperl.so.4.4 and libperl.so.4.55 will be compatible.
1129 Anyway, all this leads to quite obscure failures that are sure to drive
1130 casual users crazy. Even experienced users will get confused :-). Upon
1131 reflection, I'd say leave libperl.so in $archlib.
1135 =head2 Indentation style
1137 Over the years Perl has become a mishmash of
1138 various indentation styles, but the original "Larry style" can
1139 probably be restored with (GNU) indent somewhat like this:
1141 indent -kr -nce -psl -sc
1143 A more ambitious solution would also specify a list of Perl specific
1144 types with -TSV -TAV -THV .. -TMAGIC -TPerlIO ... but that list would
1145 be quite ungainly. Also note that GNU indent also doesn't do aligning
1146 of consecutive assignments, which would truly wreck the layout in
1147 places like sv.c:Perl_sv_upgrade() or sv.c:Perl_clone_using().
1148 Similarly nicely aligned &&s, ||s and ==s would not be respected.
1150 =head1 Upload Your Work to CPAN
1152 You can upload your work to CPAN if you have a CPAN id. Check out
1153 http://www.cpan.org/modules/04pause.html for information on
1154 _PAUSE_, the Perl Author's Upload Server.
1156 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1157 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1159 If you want your patch to appear in the F<src/5.0/unsupported>
1160 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1161 out http://www.cpan.org/CPAN.html ).
1163 =head1 Help Save the World
1165 You should definitely announce your patch on the perl5-porters list.
1166 You should also consider announcing your patch on
1167 comp.lang.perl.announce, though you should make it quite clear that a
1168 subversion is not a production release, and be prepared to deal with
1169 people who will not read your disclaimer.
1173 Here, in no particular order, are some Configure and build-related
1174 items that merit consideration. This list isn't exhaustive, it's just
1175 what I came up with off the top of my head.
1177 =head2 Adding missing library functions to Perl
1179 The perl Configure script automatically determines which headers and
1180 functions you have available on your system and arranges for them to be
1181 included in the compilation and linking process. Occasionally, when porting
1182 perl to an operating system for the first time, you may find that the
1183 operating system is missing a key function. While perl may still build
1184 without this function, no perl program will be able to reference the missing
1185 function. You may be able to write the missing function yourself, or you
1186 may be able to find the missing function in the distribution files for
1187 another software package. In this case, you need to instruct the perl
1188 configure-and-build process to use your function. Perform these steps.
1194 Code and test the function you wish to add. Test it carefully; you will
1195 have a much easier time debugging your code independently than when it is a
1200 Here is an implementation of the POSIX truncate function for an operating
1201 system (VOS) that does not supply one, but which does supply the ftruncate()
1204 /* Beginning of modification history */
1205 /* Written 02-01-02 by Nick Ing-Simmons (nick@ing-simmons.net) */
1206 /* End of modification history */
1208 /* VOS doesn't supply a truncate function, so we build one up
1209 from the available POSIX functions. */
1212 #include <sys/types.h>
1216 truncate(const char *path, off_t len)
1218 int fd = open(path,O_WRONLY);
1221 code = ftruncate(fd,len);
1227 Place this file into a subdirectory that has the same name as the operating
1228 system. This file is named perl/vos/vos.c
1232 If your operating system has a hints file (in perl/hints/XXX.sh for an
1233 operating system named XXX), then start with it. If your operating system
1234 has no hints file, then create one. You can use a hints file for a similar
1235 operating system, if one exists, as a template.
1239 Add lines like the following to your hints file. The first line
1240 (d_truncate="define") instructs Configure that the truncate() function
1241 exists. The second line (archobjs="vos.o") instructs the makefiles that the
1242 perl executable depends on the existence of a file named "vos.o". (Make
1243 will automatically look for "vos.c" and compile it with the same options as
1244 the perl source code). The final line ("test -h...") adds a symbolic link
1245 to the top-level directory so that make can find vos.c. Of course, you
1246 should use your own operating system name for the source file of extensions,
1249 # VOS does not have truncate() but we supply one in vos.c
1253 # Help gmake find vos.c
1254 test -h vos.c || ln -s vos/vos.c vos.c
1256 The hints file is a series of shell commands that are run in the top-level
1257 directory (the "perl" directory). Thus, these commands are simply executed
1258 by Configure at an appropriate place during its execution.
1262 At this point, you can run the Configure script and rebuild perl. Carefully
1263 test the newly-built perl to ensure that normal paths, and error paths,
1264 behave as you expect.
1268 =head2 Good ideas waiting for round tuits
1272 =item Configure -Dsrc=/blah/blah
1274 We should be able to emulate B<configure --srcdir>. Tom Tromey
1275 tromey@creche.cygnus.com has submitted some patches to
1276 the dist-users mailing list along these lines. They have been folded
1277 back into the main distribution, but various parts of the perl
1278 Configure/build/install process still assume src='.'.
1280 =item Hint file fixes
1282 Various hint files work around Configure problems. We ought to fix
1283 Configure so that most of them aren't needed.
1285 =item Hint file information
1287 Some of the hint file information (particularly dynamic loading stuff)
1288 ought to be fed back into the main metaconfig distribution.
1292 =head2 Probably good ideas waiting for round tuits
1296 =item GNU configure --options
1298 I've received sensible suggestions for --exec_prefix and other
1299 GNU configure --options. It's not always obvious exactly what is
1300 intended, but this merits investigation.
1304 Currently, B<make clean> isn't all that useful, though
1305 B<make realclean> and B<make distclean> are. This needs a bit of
1306 thought and documentation before it gets cleaned up.
1308 =item Try gcc if cc fails
1310 Currently, we just give up.
1312 =item bypassing safe*alloc wrappers
1314 On some systems, it may be safe to call the system malloc directly
1315 without going through the util.c safe* layers. (Such systems would
1316 accept free(0), for example.) This might be a time-saver for systems
1317 that already have a good malloc. (Recent Linux libc's apparently have
1318 a nice malloc that is well-tuned for the system.)
1322 =head2 Vague possibilities
1328 Get some of the Macintosh stuff folded back into the main distribution.
1330 =item gconvert replacement
1332 Maybe include a replacement function that doesn't lose data in rare
1333 cases of coercion between string and numerical values.
1335 =item Improve makedepend
1337 The current makedepend process is clunky and annoyingly slow, but it
1338 works for most folks. Alas, it assumes that there is a filename
1339 $firstmakefile that the B<make> command will try to use before it uses
1340 F<Makefile>. Such may not be the case for all B<make> commands,
1341 particularly those on non-Unix systems.
1343 Probably some variant of the BSD F<.depend> file will be useful.
1344 We ought to check how other packages do this, if they do it at all.
1345 We could probably pre-generate the dependencies (with the exception of
1346 malloc.o, which could probably be determined at F<Makefile.SH>
1349 =item GNU Makefile standard targets
1351 GNU software generally has standardized Makefile targets. Unless we
1352 have good reason to do otherwise, I see no reason not to support them.
1356 Somehow, straighten out, document, and implement lockf(), flock(),
1357 and/or fcntl() file locking. It's a mess. See $d_fcntl_can_lock
1358 in recent config.sh files though.
1362 =head2 Copyright Issues
1364 The following is based on the consensus of a couple of IPR lawyers,
1365 but it is of course not a legally binding statement, just a common
1372 Tacking on copyright statements is unnecessary to begin with because
1373 of the Berne convention. But assuming you want to go ahead...
1377 The right form of a copyright statement is
1379 Copyright (C) Year, Year, ... by Someone
1381 The (C) is not required everywhere but it doesn't hurt and in certain
1382 jurisdictions it is required, so let's leave it in. (Yes, it's true
1383 that in some jurisdictions the "(C)" is not legally binding, one should
1384 use the true ringed-C. But we don't have that character available for
1385 Perl's source code.)
1387 The years must be listed out separately. Year-Year is not correct.
1388 Only the years when the piece has changed 'significantly' may be added.
1392 One cannot give away one's copyright trivially. One can give one's
1393 copyright away by using public domain, but even that requires a little
1394 bit more than just saying 'this is in public domain'. (What it
1395 exactly requires depends on your jurisdiction.) But barring public
1396 domain, one cannot "transfer" one's copyright to another person or
1397 entity. In the context of software, it means that contributors cannot
1398 give away their copyright or "transfer" it to the "owner" of the software.
1400 Also remember that in many cases if you are employed by someone,
1401 your work may be copyrighted to your employer, even when you are
1402 contributing on your own time (this all depends on too many things
1403 to list here). But the bottom line is that you definitely can't give
1404 away a copyright you may not even have.
1406 What is possible, however, is that the software can simply state
1408 Copyright (C) Year, Year, ... by Someone and others
1410 and then list the "others" somewhere in the distribution.
1411 And this is exactly what Perl does. (The "somewhere" is
1412 AUTHORS and the Changes* files.)
1416 Split files, merged files, and generated files are problematic.
1417 The rule of thumb: in split files, copy the copyright years of
1418 the original file to all the new files; in merged files make
1419 an union of the copyright years of all the old files; in generated
1420 files propagate the copyright years of the generating file(s).
1424 The files of Perl source code distribution do carry a lot of
1425 copyrights, by various people. (There are many copyrights embedded in
1426 perl.c, for example.) The most straightforward thing for pumpkings to
1427 do is to simply update Larry's copyrights at the beginning of the
1428 *.[hcy], x2p/*.[hcy], *.pl, and README files, and leave all other
1429 copyrights alone. Doing more than that requires quite a bit of tracking.
1435 Original author: Andy Dougherty doughera@lafayette.edu .
1436 Additions by Chip Salzenberg chip@perl.com and
1437 Tim Bunce Tim.Bunce@ig.co.uk .
1439 All opinions expressed herein are those of the authorZ<>(s).
1441 =head1 LAST MODIFIED
1443 27-04-2007 H.Merijn Brand
1444 $Id: pumpkin.pod,v 1.23 2000/01/13 19:45:13 doughera Released $